Many CDs, especially those of classical and jazz
performances, preserve a sense of the acoustic environment in which the
recording took place. On a good two channel playback system this ambience
information is perceived as depth and width of the sound stage. The ambience
information can be extracted and fed to rear loudspeakers. Doing so increases
the apparent acoustic space around the listener and significantly enhances the
realism of reproduction and its enjoyment.

In its simplest form of implementation the difference
signal between left and right channels is taken, then delayed electrically by 15
ms to 30 ms and applied to two rear speakers. A refinement of this approach is
described by Doug Rife,
designer of the MLSSA loudspeaker and acoustic analyzer.

I have chosen a Lexicon
DC2 Digital Controller for my surround system. The DC2 is a preamplifier with
remote volume control that can take analog inputs as well as digital inputs from
CD and DVD transports. It provides up to seven outputs for
left-center-right front channels, left-right side channels, and left-right rear
channels. The unit is immensely flexible and handles not only all home theater
modes, but also provides a variety of music specific modes, including ambience
recovery from stereo recordings.

My interest is in high accuracy sound and music
reproduction. I am not using a center channel, because the main Audio Artistry
Beethoven-Elite speaker system provides excellent imaging and a center speaker
does not fit with the decor. I wanted the two side speakers and the two rear
speakers to be visually and acoustically unobtrusive. Ambience information is
played back at a lower sound level, so that small size speakers can be used, but
they should reproduce frequencies down to at least 60 Hz. Since the speakers
need to be at ear level height when seated, I made the stand part of the speaker
enclosure. The speaker cones point upwards for wide and uniform sound
dispersion. Construction details are provided on the Surround
Speaker page in the Build-Your-Own
section of this website.

The photos show the speaker setup in my living room.
Visible are the front and the two side speakers. The two rear speakers are outside the
first picture.

Most of my listening is done from the center chair at the
bottom of the above picture. For very critical listening I may turn around the
chair closest to the front speakers. The side speakers are aligned with this
chair. None of the four surround speakers
are localized as separate sound sources, even when sitting on the sofa or in the
right chair.

The left and right rear speakers are about 23 feet away
from the front speaker. All four surround speakers are
visually quite unobtrusive. More so than the photos might indicate.

The surround speakers face upward to generate a diffuse
sound field in order to prevent sharp imaging of side and rear sounds. This is
not a system for home theater, where sound effects are panned into side and rear
channels. You can see from the size of the TV that video plays a minor role in
this house.

Almost all of my music is on CD, hardly anything on DVD-Video.
"Music Logic" is my default mode for the Lexicon DC2. It can be enjoyable to listen to DVD-V
surround sound on this system, if the sound effects in the side and rear channels are kept to a
minimum. In the future I might add DVD-Audio and SACD capability, but
compared to a high quality CD the sonic improvement from 24bit/96kHz high
resolution audio is surprisingly subtle. Unless the loudspeakers and the whole
signal chain are of the highest accuracy, probably very little is gained from the new
formats. The greatest and most readily realized benefit in realism comes from
the addition of two ambience channels to a conventional stereo system.
Increasing this to four ambience channels provides a smaller gain.

After the ORION loudspeakers
had replaced the Audio Artistry Beethoven-Elite speakers in the system above
I discovered quickly that I preferred the normal 2-channel stereo playback over
the ambience recovery surround sound that I had used previously for many
recordings. The ORION gives such a natural presentation of the soundstage that
the Music Logic mode of the DC-2 actually detracted from the listening
experience. It affected imaging, sound color and bass response. Consequently, I
did not use the rear speakers for many months.

There is a vast volume of well recorded 2-channel material
on CD available. Since the ORION does such a satisfying job of playing it back,
any ambience recovery system must not change the signal to the two front
speakers. This can be assured by using a separate processor which derives the
various surround signals from the CD player output. Of those only the signals
for the side and rear speakers are then used.

This approach works exceedingly well. It adds reverberant
sound to the room and makes the walls disappear. The side
and rear speakers cannot be localized, because the signals feeding them are
decorrelated and the speakers have very wide dispersion. The rear speakers
contribute little audibly, except that without them the side speakers would have
to deliver higher output. Since all speakers use 4" drivers and are
configured as full-range speakers in the A/V receiver, it is beneficial to share
the load between them. The surround speakers need to have some bass output to
simulate ambience.
The effect is an increase in fullness of sound, without distracting from the
imaging, and actually giving instruments more body. One must be careful not to
set the volume level of the side and rear speakers too high. Their contribution
is really noticed when they are turned off and the sound turns almost flat. It
takes a while to find the correct Volume 2 level relative to Volume 1, but once
found it is always the same dB number offset between the two volume settings,
regardless of the recording. A surprising benefit of this system is that I
reduce the volume level to the front speakers by 5 dB compared to the settings
that I used in 2-channel mode. Yet the subjective loudness is unchanged and the
sound is even richer.
The setup above is slightly inconvenient because any volume change of the Preamp
requires a corresponding volume change of the A/V Receiver to keep the surround
speaker output in fixed proportion to the front speakers. If, instead, the
A/V Receiver takes its 2-channel analog input from the Preamp after Volume 1 has
been set, then Volume 2 can stay at a constant setting to provide just the right
amount of ambience.

If you have a good 2-channel sound system, then here is a
way to add to its realism. It would seem to me that the A/V receiver is not very
critical, as long as it has the proper processing capability, since only
background sounds are derived from it. Give it a try!Top

I had acquired the DPR 1001 Audio/Video receiver to experiment with
SACD and DVD-A playback, and have learned a bit more about the use of the 6
discrete channels that can be recorded in these formats. While the two storage formats have been well defined at
the bit level, there seems to be no universal agreement about what to record to the different channels,
nor about the loudspeaker layout to play them back. In particular, I read that
some recording engineers would rather not use a center channel for music, while
others insist on it. Chesky, on the other hand, proposed 2 front speakers, 2
elevated side/front speakers and 2 rear speakers. This takes up the available 6
discrete channels. A universal player like the Pioneer DV-45A has 6 analog audio outputs
for SACD or DVD-A multichannel sound recordings, which are labeled Front L/R,
Surround L/R, Center and Subwoofer. The
de-facto standard for multi-channel music playback seems to be the Home Theater
5.1 speaker setup. The multi-channel music demonstrations that I have
heard from Sony, Meridian, JBL and others used a 3+2+.1 setup and have been disappointing in
comparison to the 2+2+2 setup by Chesky/Muse/Avalon, which demonstrated DVD-A to
the High-Resolution Audio Workshop during the 106th
AES Convention in Los Angeles. The large number of installed 5.1 home theater
setups is clearly driving the music recording industry now.

Most of the SACD and DVD-A discs that I tried contained a
recorded center channel track. If this track is not used during playback, then
the sound stage has a glaring hole in the center. The DV-45A can be configured
for "no center speaker". In that case the center channel information
is mixed equally into left and right front speakers and a stable phantom image
is generated between the two speakers. But, when the sound stage is compared to
the sound stage from the 2 track mix, that is provided on the same disc, then
the 2 track version presents a more continuous image spread. Thus, I
have come to the tentative conclusion, if a center channel has been recorded, it should
also be played back via a center speaker, and not as a phantom center. This then
demands a suitable center speaker to get the most from the new discrete
multi-channel recording formats.

In order to verify my tentative conclusion I will use the top section of the ORION,
mounted on a stand, as a "small" center speaker. I do not see a need
for a full-range or "large" center speaker, since the frequency range
above 100 Hz is all that is needed to establish directional cues in this
playback situation. In my room the center speaker will only be placed in
position, when I actually listen to a SACD or DVD-A recording, since I have no
esthetically satisfactory solution for a permanent center speaker. My current surround channel speakers appear
to perform adequately for the type of music I listen to.

My center speaker prototype uses ORION midrange and
tweeter channel electronics, except that the 120 Hz highpass filters and
midrange delay circuits are bypassed. The DPR 1001 is set up for a
"Small" center speaker. The cabinet dimensions follow the drawings in
the ORION documentation, except that the dress panel is lengthened for cosmetic
reasons. I decided not to build a fully finished unit before finding out whether
I would keep a center speaker.

I have now spent
a good amount of time listening with and without the center speaker. Actually,
this speaker blends in its tonality so well with left and right speakers that I
often had to walk right up to it in order to tell whether it was on or off. My conclusions
after listening are not completely what I
expected.
First, the one time where the center speaker was of benefit occurred during
the Mahler Symphony #4 recording of the San Francisco Symphony. The words sung
by the soprano in Davies Symphony Hall were slightly better to understand.
Secondly, recordings that did not use a center channel (Chesky) were not
recognizable as such. Only by touching the speaker cone did it become apparent
that I was listening to a phantom center.
Third, switching between actual and
phantom center on recordings that used the center channel did not produce
significant audible differences. If anything, I preferred the phantom center and
the associated smoothness of soundstage spread.
Fourth, the side speakers
should have some bass output and not be "Small". The sense of acoustic
space and ambience depends strongly on the frequency range below 500 Hz. I used
two of my surround speakers on each
side in "Large" mode to keep distortion low. The distortion became
noticeable on large choral pieces.
At this point I am not convinced that a center speaker in my
system is worth it, even if it is placed out of sight most of the
time. Sitting in front of such speaker is visually highly distractive and its
benefit for multi-channel sound is marginal, given the satisfying sound stage
that is set up by the ORION.

A number of people wrote to me about the reissue of RCA
Red Seal Living Stereo recordings in SACD format and the necessity of a center
channel speaker for playback. A number of the original recordings were made with
3-track analog tape equipment for playback over left, center and right front
speakers. They were mixed down to two channels for LP issue and contained some
wonderful classical music performances. Today the original, unprocessed three
tracks of these historical recordings can be heard via SACD.

The following are first impressions and observations from
comparing playback of the 3-channel recording to the 2-channel CD down-mix which
is also on the SACD. I used the center speaker that is described above and which
was entered into the AV receiver setup as 'Small' for bass management.

1 - The CD tracks are superb on the 'Rubinstein'. I had
listened to them several times and weeks had gone by before I finally took the
center speaker out of the garage and set it up again. Well, the SACD and its
center channel added a real sense of solidity and body to the piano. Definitely
worthwhile. This motivated me to find more of the RCA recordings and I got discs
2 and 3 from the local record store.

2 - The recording quality of the 'Pictures' is far below
the 'Rubinstein'. I have not listened to the whole piece. It did not promise to
be enjoyable. Track 7, for example, has horrendous modulation distortion. I
moved on to disc 3 with trepidation.

3 - The 'Tchaikosky' immediately struck me as a clean,
natural recording and curiously I switched to the 'Rachmaninoff', which is my
wife's favorite music, thinking that I could give her a demo she would enjoy. I
was surprised about the difference in sound stage. The three microphones must
have been very widely spaced. The string sound is quite unnatural. On the CD cut
the phantom image of the piano is swimming in space. The center speaker locks it
in place and anchors the sound stage on the SACD cut. I suspect the weakness in
image stability is due to small amounts of wow and flutter from the analog tape
recorder. On such recordings a center speaker stabilizes the image, but also
tends to draw the center stage unto itself, rather than leaving it behind the
speaker. Preferably I listen with my eyes closed in order not to get my sonic
mental image distorted by the visual presence of the speakers.

All three SACD benefited from using a center speaker,
though in different degree. I then switched to two recent SACD recordings:
4 - Orff: Carmina Burana, Atlanta Symphony Orchestra and Chorus, on Telarc
5 - Mahler: Symphony #4, San Francisco Symphony

The first impression after the RCA recordings was one of
greater stability and solidness of sound. Also the low frequency end was more
realistic in its character. The center speaker seemed to contribute less to the
image other than to widen somewhat the 'sweet spot' for listening. It also had
some benefit in making the soprano in the last movement of the 'Mahler' more
intelligible, though still not enough to follow the German text. But that is not
different from a live concert. With these two recordings, though, the center
speaker was visually in the way, because the sonic event was happening behind
it. It is much more easy to ignore the left and right speakers as just sitting
there and not being part of the sound picture when I listen to a good CD, but
having three speakers looming there like a fence, though seemingly transparent,
is disconcerting to me and I must close my eyes not to get distracted.

Someone suggested to me to get the Clark Terry,
'Portraits' recording on Chesky Records to see if the trumpet can be reproduced
with a 1 inch dome tweeter crossed over at a low 1440 Hz as I do for the ORION.
This 1988 recording by Bob Katz has been
reissued on SACD. The center channel is not used and so in this respect there is
no noticeable difference between the CD and SACD tracks. The sound stage is that
of a typical studio recording as opposed to the Bucky Pizzarelli, 'Swing Live'
SACD's nightclub atmosphere, which to me is more pleasing. The trumpet does
indeed tax the tweeter more than on most recordings. For example, playing the 'Autumn Leaves'
selection of the 'Portraits', track 3, at respectably loud sound levels demands around 20
W peak from the tweeter's dedicated power amplifier. The
trumpet is firmly locked to the right speaker, the piano to the left speaker while the
bass and drums are located between the speakers with some depth and
separate from them. The trumpet sound seems slightly more bodied on the
SACD cut. I am quite certain that the trumpet sound character is not modified by
tweeter distortion. It appears level independent. Also, I have listened to many other trumpet and
brass instrument recordings (e.g. Wynton
Marsalis) at high levels without any suggestion of tweeter stress. A 20 W
requirement for the tweeter can be quite demanding, though, if a single power amplifier
must drive a loudspeaker through passive crossover networks. Then these 20 W must be
delivered on top of the simultaneously occurring and usually higher power draw from
midrange and woofer drivers. This can lead to clipping distortion and even
destruction of the tweeter unless the power amplifier has very high power
capability and headroom.
The two mentioned jazz SACD contain fun music and are well worth owning. They
are good examples of surround sound without a center channel, where the main
purpose of the surround channels is the creation of acoustic space and not the
placement of discrete instruments to the side or rear of your room.

My overall assessment for the need of a center channel
with the ORION has not changed. If I sit for my critical or fully involved listening
in the stereo 'sweet spot', the apex of an equilateral triangle,
then the contribution from the center speaker - as compared to a phantom center
- is
marginal. I only found it worthwhile for the historic RCA recordings. If I listen from a greater distance,
then the reverberant sound in the room becomes too dominant for the center speaker to make a significant
difference. If I sit off to one side, then the sound is pulled less strongly to
the near speaker, but that does not turn it into a place where I would sit to listen attentively,
because the sound stage is too distorted.

A
further observation may illustrate the pro and con of a center
speaker. I was listening to the wonderful SACD recording of Mahler's
Symphony #2 by the San Francisco Symphony - of an outstanding
performance which I had actually attended - and I noticed that the sound
of the large chorus became more aggravating during loud passages than I am
used to from 2-channel choral recordings and live performances. When I
disconnected the center speaker and set the receiver to produce a phantom
center, the sound and sound stage became smoother. The slight loss in
intelligibility of the center stage soloists was compensated for by a
generally more musical and believable image presentation without lump.

In 2-channel playback there is crosstalk from the
left speaker to the right ear and from the right speaker to the left ear,
which results in comb filtering due to time delays. The center speaker
adds additional signals at the ears that are not necessarily time coherent
with the other two speakers' signals, because of the overlap in the three
microphone pickups. This may have caused the
effect that was observed.

For the time being I will leave the center speaker in my listening room rather
than return it to the garage. I have moved it off to the right where it is
mostly out of sight. I can easily place it back in the center should the need
arise. But I suspect a center setup will not last.